An essential part of each coin operated telephone is apparatus responsive to the deposit of a coin for generating signals indicative of the value of the deposit. In one prior art coin telephone, each deposited coin strikes a distinctive gong or a chime. The sound generated thereby is converted to an electrical signal by a transducer and applied to the telephone line. An operator interprets the various sounds to determine the value of the deposited coins.
In another prior art coin operated telephone station, a switching device is included which operates one or more times in response to the deposit of each coin. Each switch operation is indicative of an incremental coin value such as five cents. Each operation of the switch energizes an oscillator that generates an electrical signal burst in the audible frequency range. These bursts are counted by the operator to determine the value of the coin deposited. A system of this type is disclosed in E. R. Andregg et al. U.S. Pat. No. 3,146,312, issued Aug. 25, 1964.
Operators working with the above-described coin identification systems are sometimes confused as to whether signals generated at a TOUCH-TONE signal dial are dial signals or coin deposit signals. Unfortunately, certain telephone users attempt to fool the operator into thinking that the requisite coins have been deposited by depressing certain combinations of the pushbuttons to generate series of single frequency tones.
J. E. Edington U.S. Pat. No. 3,428,751, issued Feb. 18, 1969, discloses one prior art arrangement that allows the operator to distinguish dial signals from coin deposit signals. In the Edington arrangement, a distinctive single frequency guard tone is provided at the termination of each dial signal. Thus, if an operator hears this guard tone, he or she then realizes that the preceding tone was generated from the pushbuttons rather than from the deposit of coins. The Edington arrangement appears to be effective in preventing the use of a TOUCH-TONE signaling dial to generate coin deposit signals.
Other prior art arrangements have attempted to automate the coin deposit detection functions normally performed by the operator. These systems are predicated on the theory that tone detectors responsive to specific frequency tones are more accurate in detecting coin deposit tones then an operator and therefore such detectors are less susceptible to fraudulently generated coin signals.
One such automated prior art system is disclosed in A. E. Joel Jr. U.S. Pat. No. 2,676,209, issued Apr. 21, 1954. In this system, each coin station includes signal generators controlled by coin deposits for generating transmitted combinations of two frequencies which identify the type of coin deposited, i.e, a nickel, a dime, or a quarter. These distinctive frequency combinations were detected by a tone detector and when the requisite coins were deposited, the call was completed without operator intervention.
Another fully automated prior art coin system is disclosed in N. R. Shaer U.S. Pat. No. 3,453,389, issued July 1, 1969. The Shaer system is incorporated in a larger partially automated traffic service position system (TSPS) disclosed in R. J. Jaeger, Jr. et al. U.S. Pat. No. 3,484,560, issued Dec. 16, 1966. This TSPS is hereinafter described in greater detail in conjunction with the present invention.
In the Shaer system the coin stations were modified as disclosed in the above-mentioned E. R. Andregg et al. patent. Now a number of tone pulses were generated for each deposited coin. One tone pulse was generated for a deposit for a nickel, two pulses for a dime, and five pulses for a quarter. Coin tone receivers were provided for detecting these series of tone pulses to identify the coin deposited in the coin station. When the requisite deposit was detected, the call was completed without operator intervention.
In still another prior art automated coin system as disclosed in copending application Ser. No. 689,600, filed May 24, 1976 by R. M. Dudonis (entitled Automated Coin Arrangement Provided Interference Free Coin Deposit Detection During Announcements), voice and other coin deposit signals received from a calling coin station are segregated from the automated announcements applied to the calling coin station. Thus, the coin tone detector can detect coin deposit tones even during announcements without any interference therewith.
All the above-mentioned prior art arrangements provide varying amounts of protection against fraud perpetrated by a subscriber at the calling coin station. Many of these arrangements are highly effective in preventing or a least indicating the existence of fraudulently generated coin deposit signals during the initial coin deposit period in which an initial deposit is deposited prior to or during the completion of the requested connection. However, all the above arrangements are susceptible in the varying extents to coin deposit signals fraudulently generated by the called station during intermediate coin deposit intervals. These intermediate coin deposit intervals are those deposit intervals in which both called and calling stations are connected together. More specifically, if the call is directed from a calling coin station to a called coin station, then coins deposited in the called coin station during intermediate coin deposit intervals may generate the same coin deposit signals as coins deposited in the calling coin station. Prior art detection equipment or an operator cannot distinguish between called station generated coin deposit signals and calling station generated coin deposit signals. Since coins can only be collected in the calling coin station, any coins deposited in the called coin station will not be collected and, accordingly, can be easily recovered by the called subscriber. Thus, the called subscriber has fraudulently derived free telephone service.
Moreover, in calls directed from a calling coin station to a regular called station, coin deposit signals can be acoustically coupled through the called station to the receiving apparatus to simulate valid coin deposit signals. Thus, apparently valid coin deposit signals can be generated at the called station and applied over the network connection during intermediate coin collection intervals to derive free use of the telephone network in these prior art systems.
It is an object of our invention to prevent fraudulently generated coin deposit signals emanating at a called station from being detected as valid coin deposit signals.
It is a further object of our invention to prevent called party fraud in automated systems for detecting coin deposit signals.